The infrared spectrum has offered possibilities beyond human visual capabilities. Infrared (IR) detectors have found their place in many applications, and have been indispensable tools for looking at objects from a different perspective to investigate less-evident properties. As a result, there has been ongoing research in IR-detector technologies, exploring different approaches with a wide range of material systems. These steady advances in technology constantly require better and more sensitive detectors for demanding applications.
The long wave infrared region, also known as the “thermal imaging” region, is the infrared region in which sensors can obtain a completely passive image of objects, based on thermal emissions only and requiring no illumination such as the sun, moon, or infrared illuminator. The classification range of long wave infrared energy varies, but typically falls between either 8 to 12 micrometers or 7 to 14 micrometers.
Infra-red detectors are used in a wide variety of applications, and in particular in the military field where they are used as thermal detectors in night vision equipment, air borne systems, naval systems and missile systems. Highly accurate thermal detectors have been produced using InSb and HgCdTe p-n junction diodes, however these thermal detectors require cooling to cryogenic temperatures of around 77 K which is costly. The cryogenic temperatures primarily are used to reduce the dark current generated in the p-n junction diode by among other effects Shockley Reed Hall (SRH) generation.
The biggest challenge for IR detectors is realization of a device that can create an adequate signal-to-noise ratio. To achieve this, the detector should efficiently absorb light at a particular wavelength. For best performance, it should have dark noise much lower than the signal noise as well as be coupled with read-out electronics that have similar low-noise properties.
In the last few years, a new detector concept had been invented and developed by Dr. Shimon Maimon [Ref. 1,2] called nBn and has become one of the most important concepts in thermal imaging. Until now, the nBn was limited to Mid Wave IR (3-5 micrometer range) using InAsSb as an absorber and AlAsSb as a barrier, with slight modifications performed on these materials for different applications. However, a good absorber material for a long wave nBn has not been developed. An absorber material for a long wave nBn device must: 1. Absorb light in the long wave range and 2. For using the AlAsSb barrier as passivation (AlAsSb was found to be the best passivation that exists today for any IR-detectors), the holes in the absorber need to be able to transport and cannot be localized as in (InAs/GaSb superlattice type-II (sls-II). Also, the barrier must stop electrons from transport between the absorber and the contact layers while at the same time allow for the transport of holes (minority carriers in the absorber) from the absorber to the contact layer.
Accordingly, a need exists for a simple fabrication process for a long wave IR detection device which will allow for a high yield of product operability. These needs and others are met within the present disclosure, which overcomes the deficiencies of previously developed long wave IR detection devices and materials.